Handle nested position:sticky elements

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 152 matching lines @@
          layoutObject->isVideo();
 }
 
 // Get the scrolling coordinator in a way that works inside
 // CompositedLayerMapping's destructor.
 static ScrollingCoordinator* scrollingCoordinatorFromLayer(PaintLayer& layer) {
   Page* page = layer.layoutObject()->frame()->page();
   return (!page) ? nullptr : page->scrollingCoordinator();
 }
 
+static WebLayer* nearestCompositedStickyLayer(
+    const StickyConstraintsMap& constraintsMap,
+    LayoutBoxModelObject* obj) {
+  while (obj && obj->compositingState() == NotComposited) {
+    DCHECK(constraintsMap.contains(obj->layer()));
+    const StickyPositionScrollingConstraints constraints =
+        constraintsMap.get(obj->layer());
+    obj = constraints.nearestStickyElementShiftingStickyBox()
+              ? constraints.nearestStickyElementShiftingStickyBox()
+              : constraints.nearestStickyElementShiftingContainingBlock();
+  }
+
+  if (!obj)
+    return nullptr;
+
+  return obj->layer()
+      ->compositedLayerMapping()
+      ->mainGraphicsLayer()
+      ->platformLayer();
+}
+
 CompositedLayerMapping::CompositedLayerMapping(PaintLayer& layer)
     : m_owningLayer(layer),
       m_contentOffsetInCompositingLayerDirty(false),
       m_pendingUpdateScope(GraphicsLayerUpdateNone),
       m_isMainFrameLayoutViewLayer(false),
       m_backgroundLayerPaintsFixedRootBackground(false),
       m_scrollingContentsAreEmpty(false),
       m_backgroundPaintsOntoScrollingContentsLayer(false),
       m_backgroundPaintsOntoGraphicsLayer(false) {
   if (layer.isRootLayer() && layoutObject()->frame()->isMainFrame())
@@ skipping 113 matching lines @@
   if (sticky) {
     if (!ancestorOverflowLayer->isRootLayer()) {
       sticky = ancestorOverflowLayer->needsCompositedScrolling();
     } else {
       sticky = layoutObject()->view()->frameView()->isScrollable();
     }
   }
 
   WebLayerStickyPositionConstraint webConstraint;
   if (sticky) {
+    const StickyConstraintsMap& constraintsMap =
+        ancestorOverflowLayer->getScrollableArea()->stickyConstraintsMap();
     const StickyPositionScrollingConstraints& constraints =
-        ancestorOverflowLayer->getScrollableArea()->stickyConstraintsMap().get(
-            &m_owningLayer);
+        constraintsMap.get(&m_owningLayer);
 
     // Find the layout offset of the unshifted sticky box within its enclosing
     // layer.
     LayoutPoint enclosingLayerOffset;
     m_owningLayer.enclosingLayerWithCompositedLayerMapping(ExcludeSelf)
         ->convertToLayerCoords(m_owningLayer.ancestorOverflowLayer(),
                                enclosingLayerOffset);
+
     FloatPoint stickyBoxOffset =
         constraints.scrollContainerRelativeStickyBoxRect().location();
     DCHECK(!m_contentOffsetInCompositingLayerDirty);
     stickyBoxOffset.moveBy(FloatPoint(-enclosingLayerOffset) -
                            FloatSize(contentOffsetInCompositingLayer()));
 
     webConstraint.isSticky = true;
     webConstraint.isAnchoredLeft =
         constraints.anchorEdges() &
         StickyPositionScrollingConstraints::AnchorEdgeLeft;
     webConstraint.isAnchoredRight =
         constraints.anchorEdges() &
         StickyPositionScrollingConstraints::AnchorEdgeRight;
     webConstraint.isAnchoredTop =
         constraints.anchorEdges() &
         StickyPositionScrollingConstraints::AnchorEdgeTop;
     webConstraint.isAnchoredBottom =
         constraints.anchorEdges() &
         StickyPositionScrollingConstraints::AnchorEdgeBottom;
     webConstraint.leftOffset = constraints.leftOffset();
     webConstraint.rightOffset = constraints.rightOffset();
     webConstraint.topOffset = constraints.topOffset();
     webConstraint.bottomOffset = constraints.bottomOffset();
     webConstraint.parentRelativeStickyBoxOffset =
         roundedIntPoint(stickyBoxOffset);
     webConstraint.scrollContainerRelativeStickyBoxRect =
         enclosingIntRect(constraints.scrollContainerRelativeStickyBoxRect());
     webConstraint.scrollContainerRelativeContainingBlockRect = enclosingIntRect(
         constraints.scrollContainerRelativeContainingBlockRect());
+    webConstraint.nearestLayerShiftingStickyBox = nearestCompositedStickyLayer(
+        constraintsMap, constraints.nearestStickyElementShiftingStickyBox());
+    webConstraint.nearestLayerShiftingContainingBlock =
+        nearestCompositedStickyLayer(
+            constraintsMap,
+            constraints.nearestStickyElementShiftingContainingBlock());
+    webConstraint.cachedComputedStickyOffset =
+        constraints.getCachedComputedStickyOffset();
   }
 
   m_graphicsLayer->setStickyPositionConstraint(webConstraint);
 }
 
 void CompositedLayerMapping::updateLayerBlendMode(const ComputedStyle& style) {
   setBlendMode(style.blendMode());
 }
 
 void CompositedLayerMapping::updateIsRootForIsolatedGroup() {
@@ skipping 3123 matching lines @@
   } else if (graphicsLayer == m_decorationOutlineLayer.get()) {
     name = "Decoration Layer";
   } else {
     ASSERT_NOT_REACHED();
   }
 
   return name;
 }
 
 }  // namespace blink